From f2cb63324a06528f87f1815f08f66093fb34045a Mon Sep 17 00:00:00 2001
From: Sadeep Madurange <smadurange@users.noreply.github.com>
Date: Sun, 12 Dec 2021 16:34:28 +0800
Subject: 4.8

---
 4/8.c | 237 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 237 insertions(+)
 create mode 100644 4/8.c

(limited to '4/8.c')

diff --git a/4/8.c b/4/8.c
new file mode 100644
index 0000000..46b0b3f
--- /dev/null
+++ b/4/8.c
@@ -0,0 +1,237 @@
+#include <ctype.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAXOP 100      /* max size of operand or operator */
+#define NUMBER '0'     /* signal that a number was found */
+#define FUNCTION '1'   /* signal that a custom op was found */
+#define ASSIGNMENT '2' /* signal that a variable was found */
+#define VARIABLE '3'   /* signal that a variable was found */
+#define MAXVAL 100     /* max depth of val and var stack */
+#define BUFSIZE 100
+#define VARCOUNT 52                            /* supported variable count */
+#define INDEX(x) (x <= 'Z' ? x - 'A' : x - 71) /* index of the variable */
+
+int sp = 0;         /* next free stack position */
+double val[MAXVAL]; /* value stack */
+
+double lout = 0;
+double varv[VARCOUNT]; /* variable value array */
+
+int bufp = 0;      /* next free position in buf */
+char buf[BUFSIZE]; /* buffer for ungetch */
+
+/* get next operator or numeric operand */
+int getop(char[]);
+
+/* push f onto value stack */
+void push(double);
+
+/* pop and return top value from stack */
+double pop();
+
+/* returns a value from stack without removing it */
+double peek();
+
+/* clears the stack */
+void clear();
+
+/* adds support for sin, exp and pow functions */
+int main(int argc, char *argv[]) {
+  int type, i;
+  double op2, op1;
+  char s[MAXOP];
+
+  while ((type = getop(s)) != EOF) {
+    switch (type) {
+    case NUMBER:
+      push(atof(s));
+      break;
+    case '+':
+      push(pop() + pop());
+      break;
+    case '*':
+      push(pop() * pop());
+      break;
+    case '-':
+      op2 = pop();
+      push(pop() - op2);
+      break;
+    case '/':
+      op2 = pop();
+      if (op2 != 0.0)
+        push(pop() / op2);
+      else
+        printf("error: division by zero\n");
+      break;
+    case '%':
+      op2 = pop();
+      if (op2 != 0.0)
+        push((int)pop() % (int)op2);
+      else
+        printf("error: division by zero\n");
+      break;
+    case FUNCTION:
+      if (strcmp("top", s) == 0) {
+        lout = peek();
+        printf("peek top: %.8g\n", lout);
+      } else if (strcmp("dup", s) == 0)
+        push(peek());
+      else if (strcmp("swp", s) == 0) {
+        op2 = pop();
+        op1 = pop();
+        push(op2);
+        push(op1);
+      } else if (strcmp("cls", s) == 0)
+        clear();
+      else if (strcmp("sin", s) == 0)
+        push(sin(pop()));
+      else if (strcmp("exp", s) == 0)
+        push(exp(pop()));
+      else if (strcmp("pow", s) == 0)
+        push(pow(pop(), pop()));
+      else
+        printf("error: unknown function %s\n", s);
+      break;
+    case ASSIGNMENT:
+      i = INDEX(s[0]);
+      if (i < 0 || i > VARCOUNT - 1)
+        printf("error: unknown symbol %s\n", s);
+      else
+        varv[i] = pop();
+      break;
+    case VARIABLE:
+      if (strcmp("lout", s) == 0)
+        push(lout);
+      else {
+        i = INDEX(s[0]);
+        if (i < 0 || i > VARCOUNT - 1)
+          printf("error: unknown symbol %s\n", s);
+        else
+          push(varv[i]);
+      }
+      break;
+    case '\n':
+      lout = pop();
+      printf("\t%.8g\n", lout);
+      break;
+    default:
+      printf("error: unknown command %s\n", s);
+    }
+  }
+
+  return 0;
+}
+
+void push(double f) {
+  if (sp < MAXVAL)
+    val[sp++] = f;
+  else
+    printf("error: stack empty\n");
+}
+
+double pop() {
+  if (sp > 0)
+    return val[--sp];
+  else {
+    printf("error: stack empty\n");
+    return 0.0;
+  }
+}
+
+double peek() {
+  if (sp > 0)
+    return val[sp - 1];
+  else {
+    printf("error: stack empty\n");
+    return 0.0;
+  }
+}
+
+void clear() {
+  for (; sp > 0; sp--)
+    ;
+}
+
+int pushb = 0;
+int pushbval = 0;
+
+int getch() {
+  if (pushb) {
+    pushb = 0;
+    return pushbval;
+  }
+  return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) {
+  pushbval = c;
+  pushb = 1;
+}
+
+void ungets(char s[]) {
+  int len, i;
+  len = strlen(s);
+  if (bufp + len - 1 >= BUFSIZE)
+    printf("ungets: too many characters\n");
+  else {
+    for (i = len; i >= 0; i--)
+      buf[bufp++] = s[i];
+  }
+}
+
+int getop(char s[]) {
+  int i, c, nc, rv;
+
+  while ((s[0] = c = getch()) == ' ' || c == '\t')
+    ;
+  s[1] = 0;
+
+  // operators or line feed
+  if (c == '\n' || c == '+' || c == '*' || c == '/' || c == '%')
+    return c;
+
+  i = 0;
+  // numbers
+  if (isdigit(c) || c == '-') {
+    // minus operator
+    if (c == '-' && !isdigit(s[++i] = c = getch())) {
+      ungetch(c);
+      s[i] = 0;
+      return '-';
+    }
+    while (isdigit(s[++i] = c = getch()) || c == '.')
+      ;
+    rv = NUMBER;
+  } else {
+    // functions and variables
+    int count;
+    for (count = 0; isalnum(s[++i] = c = getch()); count++)
+      ;
+    int islout = strncmp("lout", s, 4 * sizeof(char)) == 0;
+    if (count == 0 || islout) {
+      if (islout)
+        rv = VARIABLE;
+      else if (c != '\n' && (nc = getch()) == '=')
+        // syntax "5 A =" means "A = 5"
+        rv = ASSIGNMENT;
+      else {
+        if (c != '\n') {
+          ungetch(c);
+          ungetch(nc);
+        }
+        rv = VARIABLE;
+      }
+    } else {
+      rv = FUNCTION;
+    }
+  }
+
+  s[i] = 0;
+  if (c != EOF)
+    ungetch(c);
+
+  return rv;
+}
-- 
cgit v1.2.3